This invention relates to an earth and road roller and, in particular, to an improved roller which provides for more uniform compaction of the surface being rolled. More particularly, this invention relates to a tandem roller which has two surface treating drums positioned one after the other and cooperate together to steer the roller.
As taught in U.S. Pat. No. 3,827,819, issued to the applicant for this application and as incorporated herein by reference, there are a number of industrial situations where it is necessary to form a smooth and uniformly compacted surface. One such situation is the subsurface and finish surface of an airplane landing strip. Uniformity of compaction and surface smoothness are also of a particular importance in the construction of roads designed to carry heavy loads. The failure to achieve uniform compaction in those and other situations tends to produce uneven surface wear with use. Furthermore, irregularities in the surfacing of a road, whether caused by uneven surface wear or by inadequate surface smoothing, provide localized areas where the surface deteriorates rapidly under use.
Modern automobiles and even large trucks have greatly improved suspension and shock absorbing components which serve to provide a relatively smooth ride even over rough surfaces. However, although a ride may appear smooth to a passenger, the wheels of the vehicle are set in vertical motion by surface irregularities. The net result is that when a pneumatic rubber tire rolls over a surface irregularity which protrudes above the average road surface, the wheel momentarily leaves the surface and then lands with substantial downward force combined with a frictional drag. It has been found that such surface engagement tends to create a depression in the road surface. Similarly, when a moving wheel falls into a depression in the road surface, there is an erosion of surface material as the wheel moves out of and past the depression. Although the greatest road damage is caused by large and often overloaded trucks and trailers, small vehicles contribute to the problem. Thus, it can be seen that road surfaces should be constructed as smooth as possible.
Prior art road rollers usually include two or more large weighted drums. At least one of the drums is driven to move the roller and another drum is pivotally connected to the body of the roller so that it can be turned to steer the roller. The drums are connected to the roller body by axles which, except for the drum used to steer the roller, are maintained parallel to each other.
In one known earth roller, three drums are arranged in tandem; the front drum is used to steer the roller, while the rear and middle drums are not capable of turning, the rear drum being used to drive the roller.
Roads are typically formed of a foundation layer of relatively large stones which provide a bearing surface and drainage, an intermediate layer of small stones and binder and finally a surface layer which may be formed of a mixture containing bituminous materials. In such a road, as each layer is formed it is compacted by a road roller. Irregularities formed in the intermediate layer carry through to the bituminous layer. Even highways which are formed initially with a concrete surface oftentimes are refinished with a bituminous surface which is compacted by a road roller. It has been found that during such a refinishing operation the rough pattern typically found in the original concrete surface appears in a modified fashion in the bituminous surface when a conventional road roller is used. Conventional road rollers do not provide these surfaces with the degree of smoothness needed for long-lasting modern roads.
The invention in the above-mentioned patent (U.S. Pat. No. 3,827,819) was found to provide a solution to the problems discussed above. That patent teaches that better compaction and a smoother surface result when in a tandem roller one of the compacting drums is replaced by a pair of drums which are skewed in a side-by-side relationship relative to the line of travel of the roller. However, such a side-by-side configuration does not take advantage of the significantly more effective compacting and smoothing action of the three-axle tandem rollers described above, especially those which are adapted to exert extra heavy downward loads to high spots in the surface being rolled. Moreover, significant problems had to be overcome which are not applicable to side-by-side drums before the tandem drums could effectively be skewed. For example, the skew angle of the drums relative to each other in most applications should be maintained while the roller is turned and it is advantageous for an accommodation to be made to adjust the skew angle of the drums for different surface conditions, all of which preferably being accomplished without having to utilize and design new power plants, control mechanisms and the like.